Electrical Mobility Measurements of Fine-Particle Formation during Chamber Studies of Atmospheric Photochemical Reactions

New approaches have been applied to electrical mobility measurement of ultrafine aerosol particles in smog chamber studies of secondary aerosol formation. With several mobility classifiers operating in parallel, rapid new particle formation was followed in the photochemical oxidation of dimethyl disulfide. When foreign particles were present before reaction was initiated, multiple bursts of nucleation and oscillations in the concentrations of 3.4-nm particles were observed. Later experiments used the scanning electrical mobility spectrometer to make high-resolution particle size distribution measurements. With this measurement method, the rapid growth of nuclei from their initial appearance at 10-nm size was followed in hydrocarbon/NO_x and hydrocarbon/NO_x/SO_2 reactions. Again, multiple bursts of nucleation were observed in some experiments, and insights were gained into particle growth mechanisms.